Need advice and info on care, feeding, and release methods for rescued Mallard 3 day old ducklings.

An old fellow on a bicycle came to my house yesterday, with 5 ducklings rescued from the middle of a road. There was no mother around. Neighborhood kids had directed him to my door. I've done some research on feeding, but I want very much to prepare them for eventual release. Of course, I know I can't just dump them in some pond when they get big. Has any of you had experience in wild duck rescue? I have them inside now, and have a 10 x 10 foot dog pen for them when they no longer need an external heat source. All advice welcomed!

Thank you all again for good tips, and both the caring, and the culinary advice. Beautiful picture, Napoleon! This is what I have been feeding them: First a gruel of ground oatmeal, whole wheat, corn, walnuts. (I stopped the walnuts after I was told they can't digest them well.) Then hard boiled egg bits coated with nutritional yeast. Minced parsley and greens. Raspberries. Minced shrimp.

I would think a local feed store would have duck feed. I know that where I live, a number of farmers actually raise domesticated ducks - mostly Muscovy breed. Anyway, the folks at the feed store could probably put you in touch with a local breeder, who could tell you exactly what they need in terms of not only food, but shelter, proper temperature, etc. Old time farmers are a great resource of knowledge.